1. Field of the Invention
This invention relates to an improved catalyst for producing hydrocarbons from synthesis gas, hydrogen and carbon monoxide, and to improvements in the hydrocarbon synthesis process. Specifically, this invention relates to a catalyst comprising cobalt and ruthenium in catalytically active amounts on a titania support and a process for utilizing the catalyst that allows on-stream regeneration and cyclical operation without having to remove the catalyst from the hydrocarbon synthesis reactor.
2. The Prior Art
Methane is available in large quantities in many areas of the world. Some methane is generated from refinery applications while large amounts of methane, as the principal constituent of natural gas, are found in deposits in various areas. Methane can be used as a gas, for example, for heating purposes, and can be transported by pipeline or as a liquefied gas over long distances. Where use of the methane as a gas is not economic or the transportation of methane requires traversing oceans, the methane can be converted to a liquid which is more easily transported and may have significantly higher value than methane gas.
Conversion of methane is normally carried out in a two-step procedure involving reforming the methane to produce hydrogen and carbon monoxide, synthesis gas, and converting the synthesis gas to higher hydrocarbons, C.sub.5 +, in a Fischer-Tropsch type reaction. Both steps of the process are well known and can be readily illustrated: the first step by U.S. Pat. Nos. 1,711,036, 1,960,912 and 3,138,438; the second step by U.S. Pat. Nos. 4,477,595, 4,542,122, and 4,088,671.
This invention is concerned with the second step, the well known Fischer-Tropsch type reaction which will be referred to hereinafter as hydrocarbon synthesis.
This invention is primarily concerned with cobalt and ruthenium catalysts for hydrocarbon synthesis and both of these metals have been disclosed as being useful in such reactions, either alone, jointly, or with other materials. What has not been disclosed in the art is the combination of steps required to produce a composition that is novel and has superior catalytic properties to other cobalt, ruthenium, or cobalt-ruthenium catalysts. These properties include: improved CO conversion, improved volumetric productivity, enhanced selectivity to C.sub.5 + and lower CH.sub.4 and the ability to regenerate the catalyst at relatively low temperatures without removing it from the reactor.
U.S. Pat. No. 4,477,595 discloses ruthenium on titania as a hydrocarbon synthesis catalyst for the production of C.sub.5 to C.sub.40 hydrocarbons with a majority of paraffins in the C.sub.5 to C.sub.20 range. U.S. Pat. No. 4,542,122 discloses a cobalt or cobalt-thoria on titania having a preferred ratio of rutile to anatase, as a hydrocarbon synthesis catalyst. U.S. Pat. No. 4,088,671 discloses a cobalt-ruthenium catalyst where the support can be titania but preferably is alumina for economic reasons. U.S. Pat. No. 4,413,064 discloses an alumina supported catalyst having cobalt, ruthenium and a Group IIIA or Group IVB metal oxide, e.g., thoria. European Patent No. 142,887 discloses a silica supported cobalt catalyst together with zirconium, titanium, ruthenium and/or chromium.